B-cell lymphoma is cancer of B-lymphocytes and accounts for more than 20,000 deaths in the U.S. each year. While many patients respond to currently available therapy, there is a high rate of cancer relapse and inability for the patients o tolerate chemotherapy. Thus, there is a significant need to make available to these patients newer therapies that are more effective and better tolerated than the drugs that are currently used. Actinobac Biomed, Inc. is developing a natural biologic therapy that seeks out and kills a subset of white blood cells (WBCs). This therapy, Leukothera(R) (LtxA; leukotoxin), is a native protein derived from an oral bacterium. LtxA binds specifically to the active form of lymphocyte function associated antigen- 1 (LFA-1) and causes cell death. LFA-1 is found exclusively on WBCs, and malignant WBCs overexpress the molecule, making them ideal targets for the drug. During the phase I stage of this STTR application, we showed that 1) LtxA kills malignant B-cells using a unique mechanism of action, which involves Fas death receptor and caspase 8; 2) lymph node tissue samples from B-cell lymphoma patients express high levels of LFA-1; 3) LtxA causes complete regression of tumors in a humanized mouse model for B-cell lymphoma and results in long-term survival; 4) the drug is well-tolerated, highly active, and does not cause a neutralizing immune response in healthy dogs or a dog with naturally-occurring lymphoma, and 5) we have initiated expression and production of recombinant LtxA in a cGMP drug manufacturing facility in preparation for Investigational New Drug (IND)-enabling studies and clinical trials. Important pharmaceutical properties of LtxA include: 1) the drug works rapidly in vivo, within minutes or less; 2) doses as low as 0.5 g/kg have been shown to be highly active in animals; 3) neutralizing antibody to LtxA is not generated in healthy or diseased animals, even after repeat dosing; and 4) the high specificity of the drug allows targeting of a subset of WBCs and complete depletion of WBCs has never been observed with LtxA treatment. During this STTR phase II proposal, Actinobac will carry out IND-enabling studies that will be included in the IND application to the FDA.